Nanosphere lithography: A versatile nanofabrication tool for studies of size-dependent nanoparticle optics

Nanosphere lithography (NSL) is an inexpensive, simple to implement, inhere ntly parallel, high throughput, materials general nanofabrication technique capable of producing an unexpectedly large variety of nanoparticle structu res and well-ordered 2D nanoparticle arrays. This article describes our rec ent efforts to broaden the scope of NSL to include strategies for the fabri cation of several new nanoparticle structural motifs and their characteriza tion by atomic force microscopy. NSL has also been demonstrated to be well- suited to the synthesis of size-tunable noble metal nanoparticles in the 20 -1000 nm range. This characteristic of NSL has been especially valuable for investigating the fascinating richness of behavior manifested in size-depe ndent nanoparticle optics. The use of localized surface plasmon resonance ( LSPR) spectroscopy to probe the size-tunable optical properties of Ag nanop articles and their sensitivity to the local, external dielectric environmen t (viz., the nanoenvironment) is discussed in detail. More specifically, th e effects of nanoparticle size, shape, interparticle spacing, nanoparticle- substrate interaction, solvent, dielectric overlayers, and molecular adsorb ates on the LSPR spectrum of Ag nanoparticles are presented. This systemati c study of the fundamentals of nanoparticle optics promises to find applica tion in the field of chemical and biological nanosensors; herein, the initi al data demonstrate that LSPR spectroscopy of Ag nanoparticles can be used to sense specifically bound analytes with zeptomole per nanoparticle detect ion limits and no detectable nonspecific binding.